Evaluation of contamination of manganese in groundwater from overburden dumps of Lower Gondwana coal mines

Abstract

Inappropriate management of coal mine overburden (OB) dumps creates environmental hazards. In many countries, high concentration of Mn was observed in groundwater near the coal mine OB dump sites. Comparatively new coal mines in Barjora coalfield were chosen in this study to assess the impact of OB dumps in groundwater. Acid Digestion (AD), Toxicity Characteristics Leaching Procedure (TCLP) and Batch Leaching Test (BLT) were performed to estimate Mn concentration in OB dumps and its leaching behaviour. Shale present in OB dump has potential to leach high concentration of Mn. The aquifer in this region is mainly unconfined type and water table is very shallow. In situ soil is characterized by 44.3% sand, 37.5% silt and 18.2% clay with a saturated hydraulic conductivity of 5.58 cm/day. Column study and HYDRUS 1D numerical modelling were used to simulate the migration of Mn in vadose zone. Subsurface soil does not possess appreciable attenuating potential to retard the transport of Mn in vadose zone. HYDRUS 1D model explains that 1.6 m thick soil profile of the study area may release Mn in groundwater after 11th year and it can attain the complete breakthrough at 17th year. A groundwater contaminant transport model based on available hydrogeological data has been developed using VISUAL MODFLOW 2009.1 software. The movement of Mn in aquifer has been determined using MT3DMS code. It indicates ≃ 8 km2 area around the two Open Cast Coal Mines (OCCMs) namely OCCM 1 and OCCM 2 may suffer groundwater contamination of Mn by 2050.